A group of Wikimaniacs where leaving from Ben Gurion international airport and one of them was Chinese. He was able to explain this riddle; the robot.txt for the Chinese Wikipedia used to be both in traditional and simplified Chinese. The result was confusion for the bots of organisations like Google, Microsoft et al.

By changing the text these bots now know how to deal with the Chinese Wikipedia and this results in substantially more traffic. This fits in nicely with the graph that is produced; there is a spike and after this the growth stays on the same trajectory.

The question arises if there are more projects with similar issues.
Thanks,
GerardM